1. Field of the Invention
The present invention relates to a method and apparatus for driving a stepping motor, and more particularly, to a method and apparatus for driving a stepping motor using a micro step driving mode where an exciting current which is increased and decreased step by step is energized to each phase.
2. Related Background Art
Various instruments are driven using a motor driven by pulse signals, for example, a stepping motor. A shutter device, for example, where a shutter blade is driven to be opened and shut using the stepping motor is known as disclosed in Japanese Utility Model Application Laid-Open No. 60-140934, Japanese Patent Publication No. 6-64281 and the like. A lens barrel device where a lens is moved along an optical axis using the stepping motor is also known as proposed in Japanese Patent Application Laid-Open No. 6-250070, for example. In the above mentioned stutter device and lens barrel, driving frequency or number of driving pulses (steps) of the stepping motor is controlled so that accurate control is carried out with respect to a speed and position of opening and closing of the shutter blade or a position of the lens along the optical axis, thereby permitting more proper photographing with a camera compared with the case of using a direct current motor or the like.
As a technique of minute control of positions, a micro step driving mode is known where an energized electrical current to a coil varies step by step to stop a rotor of the motor in a position corresponding to the energized electrical current. Also known is an energizing method to a coil of a stepping motor of two-phase permanent magnet type disclosed in Japanese Patent Application Laid-Open No. 9-047088 or the like.
A typical energizing method of the micro step driving is shown in FIG. 39. In this figure, a horizontal axis shows passage of time and a vertical axis shows values of electrical currents which flows in phases A and B of coils which are shifted 90xc2x0 each other. Each electrical current value is divided into a large number of steps and periodically repeats increasing and decreasing, and energizing the electrical current of such a value in each phase step by step allows the motor to be rotatably driven in small steps.
However, in the case where such a micro step driving mode is used to drive the shutter blade, lens or other delicate instruments by the stepping motor and stop to hold the rotor of the stepping motor in the position corresponding to the energized electrical current to the coil, there is a problem that stopping positions vary due to backlash of a reduction gear of a gear or a screw or due to inertial friction of a sliding portion.
Full step driving has a higher speed of rotation and output torque of the motor than the micro step driving does, while the micro step driving obviously has a higher rotational resolution of the output shaft of the motor than the full step driving does. For this reason, in case of situating a driven object in a predetermined position, the object is driven at high speed by the full step driving when far from a target position and on the way driven by the micro step driving when close to the target position to be minutely positioned, which permits positioning at high speed and accuracy.
Alternatively, in order to start moving smoothly, the object is driven at low speed by the micro step driving at first, gradually speeded up, and from more than predetermined speed, driven at much higher speed by the full step driving, which permits smooth driving of the driven object at high speed.
Energizing when switching the driving mode of the stepping motor from the micro step driving to full step driving or vice versa during driving is disclosed in Japanese Patent Application Laid-Open No. 9-023695 and herein shown in FIG. 40. The stepping motor of PM type using a two phase permanent magnet is, for example, disclosed in Japanese Patent Application Laid-Open No. 9-331666.
This motor is configured in such a manner that cylindrically formed is a rotor in the form of the permanent magnet which is circumferentially equally divided and alternately attracted to different poles, that a first coil, a rotor and a second coil are arranged in turn axially of the rotor, that a first outer magnetic pole and a first inner magnetic pole excited by the first coil are faced to an outer surface and an inner surface of the rotor, and that a second outer magnetic pole and a second inner magnetic pole excited by the second coil are faced to the outer surface and the inner surface of the rotor, and a rotor axis as a rotary axis is taken out of the cylindrical permanent magnet.
A sectional view thereof is shown in FIG. 41. A relationship between phase of attraction of the rotor having the permanent magnet and the first outer magnetic pole and first inner magnetic pole is shifted 360xc2x0/(2xc3x97number of attracted poles) with respect to a relationship between the phase of attraction of the rotor in the form of the permanent magnet and the second outer magnetic pole and second inner magnetic pole, namely shifted 45xc2x0 in Japanese Patent Application Laid-Open No. 9-331666 which has four poles.
However, in the case where energizing of the coil is changed from the micro step driving to full step driving as shown in FIG. 40, taking the stepping motor proposed in Japanese Patent Application Laid-Open No. 9-331666 mentioned above for example, the position of the rotor at a time point T1 in FIG. 40 is as shown in FIGS. 42A and 42B, and at a time point T2 as shown in FIGS. 43A and 43B.
FIGS. 42A and 43A show sections taken along A of FIG. 41, and FIGS. 42B and 43B show sections taken along B of FIG. 41. There is a difference of 74  degree between positions of rotation of the rotor shown in FIGS. 42A and 42B and FIGS. 43A and 43B, which means that the change is not smoothly made. Therefore, vibration or step out occurs to make it impossible to smoothly drive the driven object at high speed and to position the same at high speed and accuracy.
In the case where the micro step driving mode is used to drive the lens or others by the stepping motor and stop to hold the rotor of the stepping motor in the position corresponding to the energized electrical current to the coil, there is the problem that the stopping positions vary due to the backlash of the reduction gear of the gear or screw or due to the inertial friction of the sliding portion.
As another problem of the micro step control, if a driving force is low for positioning the rotor in a position where the rotor is stopped, the rotor is influenced by the friction or driving load and cannot stop at the predetermined position, leaving a difference in stopping position. Especially, when the position of the rotor comes closer to an original position to be positioned by the micro step control, the rotational driving force becomes lower which is produced to try to position in the original position so that only a slight friction force is produced which makes it difficult to position in the original position.
On the other hand, when merely rotated, the rotor is easy to be rotated with a certain delay relative to an electrical signal even if there is the friction. Namely, if the position is delayed from the original position relative to a certain energizing condition, the driving force increases to a certain extent so that the force for trying to rotate to the original position is relatively high. For this reason, the influence of the friction is less in mere rotation compared to stopping to position in the original position as described above.
Increasing the driving force can reduce the difference in stopping position, which requires high current flown in the coil, so that there is a disadvantage of consuming high power and of heating the motor, which results in a poor characteristic.
A conventional stepping motor of a small cylindrical shape which carries out the micro step control or the like is as shown in FIG. 44. A stator 102 is configured in such a manner that a stator coil 105 is concentrically winded around a bobbin 101 which is axially fixed in a nip between two stator yokes 106, that stator teeth 106a and 106b are alternately arranged in a circumferential direction of an inner diameter of the bobbin 101 in the stator yoke 106, and that the stator yoke 106 integral with the stator teeth 106a and 106b in a casing 103.
Fixed to one of two pairs of casing 103 are a flange 115 and a bearing 108, and to the other is another bearing 108. A rotor 109 is in the form of a rotor magnet 111 fixed to a rotor axis 110 and the rotor magnet 111 makes a radial air gap with the stator yoke 106a on the stator 102. The rotor axis 110 is rotatably supported between two bearings 108.
A stepping motor driven by one coil is as shown in FIG. 46 which is often used in clocks. Reference numeral 201 denotes a rotor in the form of the permanent magnet, 202 and 203; stators, 204; a coil.
The above conventional stepping motor of small size shown in FIG. 44 has a disadvantage of having an outer shape of the motor in larger size since the casing 103, bobbin 101, stator coil 105 and stator yoke 106 are concentrically arranged on an outer periphery of the rotor. There is also a disadvantage of not increasing output of the motor since magnetic flux generated by energizing the stator coil 105 mainly passes an end surface 106a1 of the stator teeth 106a and an end surface 106b1 of the stator teeth 106b as shown in FIG. 45 and is not effectively applied on the rotor magnet 111.
In FIG. 46, the magnetic flux generated by energizing the coil is concentrated on a small gap between a stator 202 and a stator 203 and is not effectively applied on the magnet. The applicant proposes the motor which solves such problems in Japanese Patent Application Laid-Open No. 9-331555 mentioned above.
This motor as proposed is configured in such a manner that cylindrically formed is the rotor in the form of the permanent magnet which is circumferentially equally divided and alternately attracted to the different poles, that the first coil, rotor and second coil are arranged in turn axially of the rotor, that the first outer magnetic pole and first inner magnetic pole excited by the first coil are faced to the outer surface and inner surface of the rotor, and that the second outer magnetic pole and second inner magnetic pole excited by the second coil are faced to the outer surface and inner surface of the rotor, and the rotor axis as the rotary axis is taken out of the cylindrical permanent magnet.
The motor with such a configuration has high output and can reduce the outer size of the motor, but it is desired to facilitate jointing the rotor axis and permanent magnet. Further, in the above configuration, thinning of the magnet results in reducing a distance between the first outer magnetic pole and first inner magnetic pole and a distance between the second outer magnetic pole and second inner magnetic pole and thereby reducing magnetic resistance of a magnetic circuit. According to this, the electrical current flown to the first and second coils of small amount can generate much magnetic flux.
However, the motor of the type as disclosed in the Japanese Patent Application Laid-Open No. 9-331666 or the like axially requires a certain length. For this reason, recently desired is a driving transmitting device having a micro motor with an axially short length. The driving transmitting device having the micro motor with the axially short length is especially required when used as the driving transmitting device arranged in a barrel of a camera and adopted for driving the shutter blade, shutter, lens and the like.
One aspect of the invention is to provide a driving apparatus for a stepping motor using a micro step driving mode where an exciting current which is increased and decreased step by step is energized to each phase comprising:
a drive control circuit which carries out energization to each phase by a predetermined combination of energization values to each phase, said circuit partly changing the combination of the energization values to each said phase depending upon a rotational direction of a motor.
One aspect of the invention is to provide a driving control apparatus for a stepping motor having a full step energizing mode where an exciting current for step driving is energized to each phase and a micro step driving mode where a step in the full step energizing mode is divided into a plurality of steps and the exciting current which is increased and decreased step by step is energized to each phase comprising:
a switch control circuit for carrying out switching from full step energization to micro step energization and switching from the micro step energization to the full step energization at a timing such that an absolute value of an energized electrical current in each phase during the micro step energization is the same or substantially the same
One aspect of the invention is to provide a driving apparatus for a stepping motor using a micro step driving mode where an exciting current which is increased and decreased step by step is energized to each phase comprising:
a drive control circuit which carries out the energization to each phase by a predetermined first combination of the energization values to each phase or a predetermined second combination of the energization values to each phase which has a larger whole amount of energization compared to said first combination; and
a selection circuit for selecting the first combination or the second combination.
One aspect of the invention is to provide a driving apparatus for a stepping motor of two-phase PM type comprising:
memorizing means for memorizing the first micro step driving table constituted by a combined value of the PWM values energized to each phase;
calculating circuit for calculating the value of said first micro step driving table with a first function;
setting means for setting number of driving steps of the stepping motor; and
a control circuit for carrying out the micro step driving selectively by the first micro step driving table or a micro step driving table after the calculation of the value of said first micro step driving table with the first function by said calculating circuit depending upon an area in the step set by said setting means.
One aspect of the invention is to provide a driving apparatus for a stepping motor having a full step energizing mode where an exciting current for step driving is energized to each phase and a micro step driving mode where a step in the full step energizing mode is divided into a plurality of steps and the exciting current which is increased and decreased step by step is energized to each phase comprising:
memorizing means for memorizing at least a first micro step driving table;
calculating circuit for calculating the value of said first micro step driving table with a first function;
full step driving means for driving the stepping motor by full steps;
means for setting number of driving steps of the stepping motor;
means for determining whether the number of steps set by said means for setting the number of steps is larger than a predetermined number of steps set in advance;
means for commencing the micro step driving by the first micro step driving when said number of steps is determined to be larger than the predetermined number of steps;
means for switching to the full step driving after said micro step driving;
means for switching from the full step driving to a second micro step driving by the micro step driving table after the calculation of the value of first micro step driving table with the first function by said calculation means after the switching by said means for switching.
One aspect of the invention is to provide a driving force transmitting apparatus comprising:
a first driving device having a magnet which is, at least at an outer peripheral surface thereof, circumferentially divided and alternately attracted to different poles to be rotatable, a gear provided integrally with said magnet and having teeth of number corresponding to the number of attracted poles of the magnet, a coil aligned with said magnet in the axial direction, a stator faced, at an outer magnetic pole portion and an inner magnetic pole portion excited by a coil, to an outer surface and an inner surface of said magnet;
a second driving device having a magnet which is, at least at an outer peripheral surface thereof, circumferentially divided and alternately attracted to different poles to be rotatable, a gear provided integrally with said magnet and having teeth of number corresponding to number of attracted poles of the magnet, a coil aligned with said magnet in the axial direction, a stator faced, at an outer magnetic pole portion and a inner magnetic pole portion excited by said coil, to an outer surface and an inner surface of said magnet; and
a transmitting mechanism having a gear portion in mesh with a gear of said first driving device and said second driving device.
One aspect of the invention is to provide a driving force transmitting apparatus comprising:
a first driving device having a magnet which is, at least at an outer peripheral surface thereof, circumferentially divided and alternately attracted to different poles to be rotatable, a gear provided integrally with said magnet, a coil aligned with said magnet in the axial direction, a stator faced, at an outer magnetic pole portion and a inner magnetic pole portion excited by a coil, to an outer surface and an inner surface of said magnet;
a second driving device having a magnet which is, at least at an outer peripheral surface thereof, circumferentially divided and alternately attracted to different poles to be rotatable, a gear provided integrally with said magnet, a coil aligned with said magnet in the axial direction, a stator faced, at an outer magnetic pole portion and a inner magnetic pole portion excited by said coil, to an outer surface and an inner surface of said magnet; and
a transmitting mechanism having a gear portion in mesh with a gear of said first driving device and said second driving device.
Further objects of the present invention will become clear from the following description of the embodiments taken in conjunction with the accompanying drawings.